Improvement in the performance of a photographic image is greatly improved upon imagewise release of a photographically useful reagent simultaneously with the formation of the silver image is known. For instance, DIR couplers in the field of color photographic light-sensitive materials are examples. DIR couplers function to improve graininess of the color image, improve sharpness due to an edge effect and improve color reproducibility due to the diffusion of an inhibitor into other layers by release of a developing inhibitor upon coupling with an oxidation product of a color developing agent at development. DIR couplers are described in detail, for example, in U.S. Pat. Nos. 3,227,554 and 4,248,962, JP-B-58-9942 (the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-B-51-16141, JP-A-52-90932 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-56-114946, JP-A-57-154234, JP-A-58-188035, JP-A-57-151944 and JP-A-58-217932.
Also, recently an improvement in the graininess of the color image or an increase in sensitivity can be achieved by using couplers capable of releasing a competing compound, a development accelerator or a fogging agent upon coupling with an oxidation product of a color developing agent as described, for example, in British Patent 1,546,837, U.S. Pat. No. 3,408,194, JP-A-57-138636, JP-A-57-150845, JP-A-59-50439 and JP-A-59-170840.
Further, colored couplers having an azo dye moiety as a releasing group are employed for the purpose of improving color reproducibility by a masking effect. More specifically, azo dyes released imagewise in the image areas upon coupling with an oxidation product of a color developing agent leach into a processing solution and are removed, and in consequence, colored couplers having an azo dye remain in the non-image areas, as described in detail, for example, in JP-A-51-26034, JP-A-51-110328, U.S. Pat. No. 4,004,929, are British patent 1,443,875 and 1,464,361.
As described above, functional couplers capable of releasing a photographically useful reagent markedly contribute to an improvement in the image quality of the color image and sensitivity. However, these functional couplers have a fundamental defect in that they can not be utilized in the field of photography wherein a color developing agent is not employed, for example, black-and-white photography and diffusion transfer photography, because they release a photographically useful reagent upon coupling with an oxidation product of a color developing agent. Further, they have another problem in that azomethine dyes formed adversely affect the color reproducibility of color image. In this respect, non-color forming DIR couplers as described for example, in JP-A-49-77635 and JP-A-50-20725 and dye runaway type couplers as described, for example, in JP-A-59-168444 have been proposed. However, problems, which arise because they have a low coupling activity and because they cause severe contamination of a processing solution, are not yet solved.
In order to solve the problems of these functional couplers, redox compounds capable of releasing a photographically useful reagent irrespect of a kind of developing agent have been eagerly sought, but they are still insufficient. More specifically, DIR hydroquinones as described, for example, in JP-A-49-129536, U.S. Pat. Nos. 3,379,529, 3,620,746, 4,322,878 and 4,377,634, DIR aminophenols as described, for example, in JP-A-52-57828, p-nitrobenzyl derivative as described, for example, in European Patent 45,129, hydrazine derivatives as described, for example, in U.S. Pat. No. 4,684,604, and redox compounds having at least one carbonyl group as described, for example, in JP A-61-213847 are known. However, these compounds have problems because some of them only have a low releasing speed for the photographically useful reagent and because those having a high releasing speed are unstable during storage. Thus, improvement has been desired.
On the other hand, in the photomechanical process field, development of a photographic light-sensitive material having good reproducibility of the original has been required in order to cope with the diversity and complexity of printed materials. A method using a redox compound as described, for example, in JP-A-61-213847 is known, but the method is still insufficient since dot gradation is elongated.
In order to solve this problem, a method using a hydroxamic acid derivative as described in Japanese Patent Application No. 63-98803 has been proposed. Although some improvement has been made, still a further increase in a release speed of photographically useful reagent and improvement in preservability thereof are still required in order to particularly fulfill the requirement of reducing the pH of a developing solution for the purpose of increasing processing stability or further shortening a processing time.